This invention relates generally to the preparation of alpha-olefin oligomer oils having a high viscosity, and particularly to methods for preparing oligomer oils, which are useful in lubricants and functional fluids, by polymerizing an olefin having 6 or more carbon atoms in the presence of a catalyst prepared by reacting an aluminum halide such as AlCl.sub.3 with a proton source, such as an alcohol, in an organic solvent.
Synthetic oils having high viscosities of about 30 centistokes or above at 100.degree. C. have been prepared by using aluminum halide catalyst systems to oligomerize alpha-olefins having about 6 to 20 carbon atoms. Such oils possess a good stability to shearing, a low pour point, and a high viscosity index. A number of aluminum halide catalyst systems have been disclosed for this purpose. U.S. Pat. No. 3,637,503 discloses a lubricating oil composition containing a viscosity index improving amount of a polymer obtained by polymerizing a normal alphaolefin having from 4 to 16 carbon atoms in the presence of a mixture of aluminum chloride and a nonpolymerizing hydrocarbon diluent. The mixture is preferably contacted with gaseous hydrogen chloride as a promoter by bubbling the gas through the solvent containing the aluminum chloride prior to introducing the olefin monomer. We have found that the viscosity of the product polyolefin oil is very sensitive to the ratio of hydrogen chloride to aluminum chloride. It would be difficult to control this ratio to the extent necessary to provide oligomer products of a selected viscosity using gaseous hydrogen chloride according to the process of U.S. Pat. No. 3,637,503. U.S. Pat. No. 4,107,080 discloses the preparation of an oligomerization catalyst suitable for the preparation of low viscosity olefin polymers in which aluminum halide is contacted with a fatty acid with complete removal of the hydrogen halide which is generated. U.S. Pat. No. 4,006,199 describes a catalyst system using aluminum halides in conjunction with dicarbonyl compounds to give olefin oligomers having a kinematic viscosity between 500-1500 cSt at 37.6.degree. C. U.S. Pat. No. 4,219,691 discloses the preparation of olefin oligomer in the presence of an aluminum halide and a secondary or tertiary alcohol. The optional use of a solvent in the oligomerization reaction for reducing the viscosity increase and easy control of the reaction temperature is suggested. Comparative i0 examples using primary alcohols gave relatively low viscosity products e.g. less than 500 centistokes at 37.8.degree. C. U.S. Pat. No. 2,631,176 discloses the preparation of high viscosity olefin polymers using a Friedel-Crafts catalyst in the presence of an oxygenated compound such as an aliphatic alcohol. The preparation of a polymer of 1-deoene in the presence of n-heptane, AlCl.sub.3 and about 2 moles of methanol per mole of AlCl.sub.3 (excess methanol) is described. The polymer had a 210.degree. F. viscosity of 232 SUS or only about 50 centistokes. We have discovered a process which can provide, with good selectivity, very high viscosity olefin oligomer fluids using a catalyst composition, which includes aluminum halide in combination with primary (as well as secondary and tertiary) alcohols or other proton donor compounds, by preparing the catalyst composition in the presence of an organic solvent using an excess of aluminum halide.